[dcolkitt]

If the co-founder doesn't think there will be a need for any new funding, then that would imply that he expects the company to be cash-flow positive in the near-term.

I'd sit down and work out what are the cash flow forecasts and milestones. Contextualize what's a reasonable rate of return for implicitly funding the company by foregoing an immediate cash buyout. If/when the company achieves certain profitability milestones, then the note will pay back in installments.

Each successful milestone draws down the principal, each missed milestone increases the principal. If profitability isn't sustainably achieved, the note converts back into common equity. If/when there's a major funding event, the note converts to common equity or cash equivalent of the common equity valuation.

Essentially you're planning for three scenarios. 1) The business becomes profitable without further funding. You're paid off over time from the profits. 2) The business goes the fundraising route. You're paid off at the liquidity event. 3) The business succeeds at neither route. Your share of the equity reverts back to you, so you receive your fair share of the scraps.